1. Field of the Invention
The present invention relates to a method of mounting a plate in a grand piano, and more particularly, to a method of mounting a plate on a base assembly of a grand piano in which an outer rim, a sound board, and so on have already been assembled.
2. Description of the Related Art
A plate of a grand piano comprises a back mechanism together with a back assembly comprised of an outer rim, a soundboard and so on, and serves to support tensions applied to strings attached therein. FIGS. 1 and 2 show an example of a conventional method of mounting a plate on a back assembly. The illustrated back assembly comprises an outer rim 2, a backpost (not shown) and a back beam 3, which have been integrally assembled, a soundboard 4 adhered to overlay the top surfaces of these components, and so on. The soundboard 4 has been previously mounted with a long bridge 5 and a short bridge 6 on its top surface, and a plurality of sound ribs (not shown) on its bottom surface. Also, the soundboard 4 is forcedly dried before the ribs are mounted, and left in a normal state after the ribs are mounted to cause the top surface side to swell due to restrictions imposed by the sound ribs, so that a crown has been previously formed. The long bridge 5 and the short bridge 6, in turn, have respective predetermined lengths, and have been individually worked. Specifically, each bridge is shaved on the top surface at locations at which strings are fixed (hereinafter called the "bridge shaving") and bridge pins are struck into the bridge hooking strings (hereinafter called the "bridge pin striking"). The bridges 5, 6 are adhered on the top surface of the soundboard 4 after such working has been completed individually on the respective bridges.
For mounting a plate 7 on the back assembly 1 constructed as described above, a set of holes consisting of dowel holes 8a on both sides, and a lower hole 8b in the middle of the dowel holes 8a are drilled, for example, by means of a three-fluted drill fixed to an NC machine, from the top surface of the soundboard 4 deep into the middle of the inner rim 2 at a plurality of predetermined positions along the outer periphery of the top surface of the back assembly 1. In this event, as shown in FIG. 2, the depth of the dowel holes 8a is set with reference to the bottom surface of the inner rim 2, such that the height of the dowel holes 8a from the bottom surface of the inner rim 2 to the bottom of the dowel holes 8a is equal to a predetermined constant height H. Next, after a dowel 9 having a predetermined length L is driven deep into the bottom of each dowel hole 8a, the plate 7 is carried on the dowels 9, and mounting screws 11 are inserted into bolt holes 10 and the lower hole 8b previously formed through the plate 7, and fastened to mount the plate 7 on the back assembly 1. In this way, an installation height HF of the plate 7 (from the bottom surface of the inner rim 2 to the bottom surface of the plate 7) is set to a constant value equal to the sum of the height H of the bottom of the dowel holes 8a and the length L of the dowels 9 (HF=H+L).
As described above, the long bridge 5 and the short bridge 6 are set at a predetermined thickness, and the installation height HF of the plate 7 is set at a constant value to allow a bridge pressure (a relative height between strings stretched on the plate 7 and the top surface of the long bridge 5 and the short bridge 6) to be controlled to some extent. As a result, it is possible to eliminate a time-consuming bridge pressure adjustment (which involves planing the top surface of the long bridge 5 or the like for achieving an appropriate bridge pressure after the soundboard 4 has been mounted on the inner rim 2), which has been traditionally performed.
While the foregoing conventional plate mounting method can relatively accurately set the installation height HF of the plate 7 with reference to the bottom surface of the inner rim 2, the method encounters significant difficulties in correctly controlling the shape of the crown since it is formed by the swelling of the soundboard 2 itself, as stated above, and the heights of the long bridge 5 and the short bridge 6 from the bottom surface of the inner rim 2 may vary in accordance with the amount of the swelling. Thus, the heights of the long bridge 5 and the short bridge 6 inevitably vary from one piano to another, and as a result, the bridge pressure, determined by a relative height relationship between the long bridge 5 and the short bridge 6 and the plate 7, also varies from one piano to another, causing a problem that an appropriate bridge pressure cannot be ensured.